Transcranial Magnetic Stimulation Reveals Two Cortical Pathways for Visual Body
Processing
Beatriz Calvo-Merino1
Co-authors: Cosimo Urgesi2, Patrick Haggard1 and Salvatore Aglioti2.
1
Institute of Cognitive Neuroscience, University College London. London, UK
2
Universidad La Sapienza, Rome, Italy.
Perception of human bodies is impaired when viewed upside down, suggesting that it
relies upon configural processing. Neuroimaging studies have identified a large frontotemporo-parietal network which is specifically involved in the visual processing of
human bodies. The neural underpinnings of configural processing of bodies, however, is
still unclear. Here we used repetitive transcranial magnetic stimulation (rTMS) to study
the causal role of premotor, visual, and parietal areas in configural processing of body
forms. Eighteen participants performed a delayed matching-to-sample task with upright
or inverted static body postures. Event-related rTMS was applied 150 ms after the sample
stimulus onset over left ventral premotor cortex (vPMc), right extrastriate body area
(EBA), and right superior parietal lobe (SPL). Additionally, rTMS was applied to right
primary visual cortex (V1) as control site. Stimulation of vPMc significantly reduced
accuracy of matching judgments for upright pictures. Interestingly, EBA rTMS
significantly impaired matching accuracy for inverted but not for upright pictures.
Furthermore, a significant body inversion effect was observed after EBA and V1 rTMS,
but not after vPMc and SPL rTMS. These results show that activity in classical mirrorsystem areas is required for the configural processing of bodies. This suggests an
embodiment of observed postures during configural processing of the human body. In
contrast, EBA appears to be involved in the analytic processing of the body, possibly
based on the form of individual body parts, instead of a whole body unit. Therefore, we
propose two distinct routes for processing visual body-form information in the human
brain.